D2D (Device-to-Device, device to device) communication technology is a novel technology allowing terminals (i.e., user equipment, which is hereinafter referred to as UE) to directly communicate with each other by multiplexing resources in a cell under control of a cellular system. In this way, control of a base station or an access node is not required, and thus communication or networking is quite flexible.
Introduction of a terminal self-organization communication mode (a D2D communication mode) for UEs of a cellular mobile communication system has a series of advantages. First, a local service for quite short distance may be completed by relaying among UEs directly without passing a base station, thereby reducing occupancy of resources of the base station. Second, a coverage flaw of a preset network can be made up, thereby eliminating some dead zones which always exist in a coverage area of an existing cellular mobile communication system. Third, power consumption can be reduced. Forth, due to the introduction of the terminal self-organization communication mode, capacity of the entire mobile communication system is increased.
With respect to a hybrid networking mode of a cellular network and D2D communication in the prior art, as shown in FIG. 1, a BS and UE1 perform transmission by the cellular network, and UE2 and UE3 perform transmission by means of D2D. It is illustrated by taking that the BS and the respective UEs are all configured with two antennas as an example. As shown in FIG. 2, the BS transmits downlink data steams s1 and s2 to the UE1 through the cellular network, wherein precoding vectors are v1 and v2; and the UE2 transmits data steam s3 to the UE3 through D2D, wherein a precoding vector is v3.
In this case, a signal y1 received by the UE1 is as follows:
      y    1    =                              H          11                ⁡                  [                                                                      v                  1                                                                              v                  2                                                              ]                    ⁡              [                                                            s                1                                                                                        s                2                                                    ]              +                  H        21            ⁢              v        3            ⁢              s        3            
wherein H11 is a channel from the BS to the UE1, and H21 is an interference channel from the UE2 to the UE1.
A signal y2 received by the UE3 is as follows:
      y    2    =                              H          12                ⁡                  [                                                                      v                  1                                                                              v                  2                                                              ]                    ⁡              [                                                            s                1                                                                                        s                2                                                    ]              +                  H        22            ⁢              v        3            ⁢              s        3            
wherein H12 is an interference channel from the BS to the UE3, and H22 is a channel from the UE2 to the UE3.
System capacity and spectral efficiency can be increased according to the above-mentioned method for transmitting a data stream, however, since the UE1 is configured with the two antennas, the UE1 can not decode the received signal y1 to obtain s1 and s2; and similarly, since the UE3 is configured with the two antennas, the UE3 can not decode the received signal y2 to obtain s3.